1. Field of the Invention
The present invention relates to a semiconductor laser apparatus capable of emitting a plurality of light beams respectively having different wavelengths.
2. Description of the Background Art
Conventionally, semiconductor laser devices emitting infrared light beams having wavelengths of approximately 780 nm (infrared semiconductor laser devices) have been used as light sources for compact disk (CD)/compact disk-recordable (CD-R) drives. Further, semiconductor laser devices emitting red light beams having wavelengths of approximately 650 nm (red semiconductor laser devices) have been used as light sources for conventional digital versatile disk (DVD) drives.
On the other hand, DVDs capable of recording and reading using blue-violet light beams having wavelengths of approximately 405 nm have been developed in recent years. In order to record and read such DVDs, DVD drives using semiconductor laser devices emitting blue-violet light beams having wavelengths of approximately 405 nm (blue-violet semiconductor laser devices) have been also simultaneously developed. In these DVD drives, compatibilities with conventional CD/CD-Rs and DVDs are required.
In this case, compatibilities with conventional CDs, DVDs, and new DVDs are realized by methods of providing a plurality of optical pickup apparatuses respectively emitting infrared light beams, red light beams, and blue-violet light beams to the DVD drives or methods of providing infrared semiconductor laser devices, red semiconductor laser devices, and blue-violet semiconductor laser devices within one optical pickup apparatuses. Since the number of components is increased in these methods, however, it is difficult to miniaturize the DVD drives, simplify the configurations, and reduce the costs.
In order to prevent the number of components from being thus increased, it is effective to provide a plurality of semiconductor laser devices emitting laser beams having different wavelengths in one packages. In this case, in order to improve extraction efficiency of the laser beams and reduce aberration, the respective positions of emission points of the laser beams must be brought near each other.
JP 2004-207479A discloses a semiconductor laser apparatus in which the distance between respective emission points of laser beams is small. In the semiconductor laser apparatus disclosed in JP 2004-207479 A, two light emitting devices respectively emitting laser beams having different wavelengths adhere to each other such that their laser cavities are opposed to each other. Thus, the distance between the respective emission points of the laser beams is reduced.
When the two semiconductor laser devices each having a ridge structure adhere to each other, as disclosed in JP 2004-207479 A, however, the following problems arise. Description is now made using the drawings.
FIG. 12 is a schematic sectional view showing an example of a conventional semiconductor laser apparatus comprising two semiconductor laser devices each having a ridge structure.
A semiconductor laser apparatus 1E shown in FIG. 12 comprises a semiconductor laser device 600 and a semiconductor laser device 700.
The semiconductor laser device 600 has an n-type semiconductor layer 61 and a p-type semiconductor layer 62 on an upper surface of a substrate 60. A ridge Ri1 is formed on an upper surface of the p-type semiconductor layer 62. An insulating layer 63 is formed in a region excluding an upper surface of a ridge Ri1 on the upper surface of the p-type semiconductor layer 62. A p-side pad electrode 64 is formed so as to cover the insulating layer 63 and the upper surface of the ridge Ri1. An n-electrode 65 is formed on a lower surface of the substrate 60.
A voltage is applied between the p-side pad electrode 64 and the n-electrode 65 in the semiconductor laser device 600 so that a first laser beam is emitted from a region (hereinafter referred to as a first emission point) 66 below the ridge Ri1 on a junction interface of then-type semiconductor layer 61 and the p-type semiconductor layer 62.
The semiconductor laser device 700 has an n-type semiconductor layer 71 and a p-type semiconductor layer 72 on a lower surface of a substrate 70. A ridge Ri2 is formed on a lower surface of the p-type semiconductor layer 72. An insulating layer 73 is formed in a region excluding a lower surface of the ridge Ri2 on the lower surface of the p-type semiconductor layer 72. A p-side pad electrode 74 is formed so as to cover the insulating layer 73 and the lower surface of the ridge Ri2. An n-electrode 75 is formed on an upper surface of the substrate 70.
A voltage is applied between the p-side pad electrode 74 and the n-electrode 75 in the semiconductor laser device 700 so that a second laser beam is emitted from a region (hereinafter referred to as a second emission point) 76 above the ridge Ri2 on a junction interface of the n-type semiconductor layer 71 and the p-type semiconductor layer 72.
The semiconductor laser device 600 and the semiconductor laser device 700 are joined to each other such that the ridge Ri1 and the ridge Ri2 are opposed to each other with a solder H.
Here, in a case where the semiconductor laser device 600 and the semiconductor laser device 700 are joined to each other, as described above, the ridge Ri1 and the ridge Ri2 come into contact with each other so that stresses are respectively applied to the ridges Ri1 and Ri2. Thus, the respective characteristics of the ridges Ri1 and Ri2 are degraded. As a result, the reliability of the semiconductor laser apparatus 1E is reduced.
Since the contact area between the ridge Ri1 and the ridge Ri2 is small, the semiconductor laser device 700 cannot be stabilized on the semiconductor laser device 600. Thus, the semiconductor laser device 700 may, in some cases, be joined to the semiconductor laser device 600 in an inclined state, as shown in FIG. 13. As a result, the position of the emission point varies for each semiconductor laser apparatus 1E.
As shown in FIG. 14, a part of the solder H is detoured around respective side surfaces of the n-type semiconductor layer 61 and the p-type semiconductor layer 62 in the semiconductor laser device 600 at the time of joining so that a short may occur. Although a wire W for applying a voltage is connected to the p-side pad electrode 64 in the semiconductor laser device 600, the melted solder H flows out to the vicinity of an end of the p-side pad electrode 64 so that defective connection of the wire W may occur.
Furthermore, in a case where the semiconductor laser apparatus 1E in which the solder H flows out to the end of the p-side pad electrode 64, as shown in FIG. 14, is joined to a sub-mount 800, which is an L shape in cross section, with the semiconductor laser device 700 positioned on its lower side, as shown in FIG. 15, the semiconductor laser apparatus 1E may, in some cases, be joined in an inclined state with respect to the sub-mount 800 by the effect of the solder H. Thus, the manufacturing yield of the semiconductor laser apparatus 1E is reduced.